The present invention generally relates to a laser diode unit, and more particularly, to a method of mounting a laser diode unit on an optical pick-up for use in an optical disk player and the like, through proper positioning and fixing.
In FIG. 6, there is illustrated a conventional laser diode unit 100 to be incorporated in an optical pick-up for use in an optical disk player or the like. The laser diode unit 100 includes a stem 101, and three lead terminals 102, 104 and 106 extending through the stem 101 in a direction of its thickness, with upper ends thereof projecting from the upper surface of the stem 101. The lead terminal 102 has its projecting upper end electrically connected with a laser diode 108 for feeding electric current to the laser diode 108, while the lead terminal 104 has its projecting upper end also electrically connected with a photo-diode 110 for deriving therethrough, electric current to be outputted from a photo-diode 110.
More specifically, the laser light emitted from the laser diode 108 is received by the photo-diode 110, and electric current proportional to an amount of light thus received is applied from the photo-diode 110 to the lead terminal 104.
Accordingly, it becomes possible to automatically control the light emitting power (referred to as APC i.e. Automatic Power Control) of the laser diode 108 based on values of the above electric current.
Meanwhile, the lead terminal 106 has a function to subject the laser diode 108 and the photo-diode 110 to connection for grounding.
A ring-shaped or annular connecting member 112 is integrally attached around the stem 101, and a cap 113 in a cylindrical shape having a bottom portion open at its one end is mounted on the connecting member 112 for enclosing the laser diode 108, etc. within the laser diode unit 100. The stem 101 and the connecting member 112, and the connecting member 112 and the cap 113 are respectively combined into one unit by resistance welding or the like.
The bottom portion of the cap 113 is formed with a window opening 113A which is closed by a glass cover 114. Therefore, the laser light emitted by the laser diode 108 is projected outwardly through the window 113A.
The known laser diode unit 100 having the construction as described above is filled in its interior, generally with an inert gas such as nitrogen gas or the like to prevent oxidation particularly at the light emitting end face of the laser diode 108.
However, in the conventional laser diode unit 100 as described so far, there are such disadvantages that, because the respective lead terminals 102, 104 and 106 are fixed to the stem 101 through hermetic sealing, manufacturing cost is increased as a result.
Moreover, the glass cover 114 to be fitted in the window opening 113A of the cap 113 is applied with an AR coating (Anti-Reflex Coating) for reduction of the reflection rate of the laser light by the glass cover 114. Thus, another cost increase is involved by such an AR coating processing.
Furthermore, due to the fact that a portion where one end of a wire for connecting the lead terminal 102 and the laser diode 108 are bonded, is gold-plated, with the stem 101 being plated by nickel, gold, etc., a further cost increase is also undesirably caused thereby.
Accordingly, there has been proposed, by the same assignee as in the present invention, another laser diode unit of this kind in which essential functioning portions such as the laser diode, photo-diode, etc. are provided on a sub-mount base, while the sub-mount base is mounted and fixed on a substrate provided with lead portions electrically connected to external circuits.
Incidentally, in the case where a laser diode unit is to be incorporated, through positioning and fixing, into an optical pick-up, allowance for the installation is limited only to several .mu.m, and thus, a high accuracy is required for the mounting and incorporation. In the conventional laser diode unit 100, such incorporation is effected by fitting the unit 100 into a mating part provided on the side of the optical pick-up. However, in the laser diode unit proposed by the same assignee as in the present invention and referred to above, it is difficult to adopt the conventional practice for incorporation due to difference in the construction. Accordingly, there may be considered processing such as brazing, bonding by resins, etc., each of which, however, involves problems related to the accuracy or the long processing time required.